Systems and methods for gas treatment

ABSTRACT

A system and process for the recovery of at least one halogenated hydrocarbon from a gas stream. The recovery includes adsorption by exposing the gas stream to an adsorbent with a lattice structure having pore diameters with an average pore opening of between about 5 and about 50 angstroms. The adsorbent is then regenerated by exposing the adsorbent to a purge gas under conditions which efficiently desorb the at least one adsorbed halogenated hydrocarbon from the adsorbent. The at least one halogenated hydrocarbon (and impurities or reaction products) can be condensed from the purge gas and subjected to fractional distillation to provide a recovered halogenated hydrocarbon.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a division of U.S. patent application Ser. No.14/717,217, filed May 20, 2015, which is itself a division of U.S.patent application Ser. No. 13/393,692, filed May 18, 2012 (now U.S.Pat. No. 9,039,808, issued May 26, 2015), which is a national phase ofInternational Application No. PCT/CA2010/001366, filed Aug. 31, 2010,which claims the benefit of U.S. Provisional Patent Application No.61/239,051, filed Sep. 1, 2009, all of which are incorporated herein byreference in their entirety.

FIELD

The present application relates generally to the recovery of halogenatedhydrocarbons from a gas stream. Generally speaking the recovery is forthe purpose of the extension of their life cycle or disposal. Moreparticularly, the present application relates to the recovery from a gasstream by adsorption; subsequent desorption and recovery from thedesorption gas by condensation; and subsequent separation andpurification by fractional distillation of halogenated hydrocarboninhalation anesthetics.

BACKGROUND

Halogenated hydrocarbon compounds include the families of compounds:bromo-, fluoro- and/or chloro-ethers, fluorinated alkyl ethers,chlorofluorocarbons and chlorofluoro ethers and their derivatives. Thesefamilies of compounds are typically used as solvents, refrigerants,anesthetics, aerosol propellants, blowing agents and the like. Many ofthese compounds are widely used and are routinely discharged into theatmosphere. Particularly in the case of medical anesthetic gases, ifthese compounds could be recovered, retrieved and purified to medicalstandards there would be a considerable cost saving and reduction inenvironmental pollution. In view of the possible negative effects ofhalogenated hydrocarbons that are released into the atmosphere, attemptshave already been made to recover such gases.

In view of the rising costs of the inhalation anesthetics and theenvironmental effects (e.g. toxic greenhouse and ozone depletion) of thedrugs, attempts are being made to recover the inhalation anestheticsbefore the anesthetics are discharged into the atmosphere. A system canbe provided for recovering inhalation anesthetics from gas streamsexiting anesthetic gas machines (which may include patient exhalentfollowing administration to a patient) by capturing scavenged gascontaining the anesthetic rich gas stream, removing water vapor and thenextracting the anesthetic using either a cryogenic process in which thevapors of the anesthetics are condensed to liquid phase, or an adsorbentmaterial which is processed later to remove the anesthetics. Thecollected liquid anesthetics can then be reintroduced directly into ananesthetic gas machine. Such approach has little if any facility tocontrol bacterial contamination and potentially recycles harmfulmicroorganisms to another patient or the anesthetic gas machine ingeneral. Additionally, there is no assurance that the condensed drugsare separated into individual components and that each recycled drugmeets the appropriate medical standards and regulations.

In another approach for recovering inhalation anesthetics, an adsorbentmaterial in an appropriate container is used to adsorb the inhalationanesthetics from the gas stream exiting the anesthetic gas machine. Whenthe adsorbent material is saturated, the container is removed and placedin a regeneration system. A purging gas, such as steam, is used toremove the anesthetics from the adsorbent material. The purged gas isthen collected, water is removed therefrom, and the anesthetics arecondensed and subjected to fractionation to separate out the individualanesthetics. Such an approach can be difficult as steam, having anelevated temperature, can cause catalytic reactions with the adsorbentand adsorbate leading to a product breakdown and pure yields of therecovered anesthetics. Furthermore, such an approach can be difficultbecause a number of different inhalation anesthetics may be used in oneoperating room and each inhalation anesthetic may require differentadsorbents and differing desorption requirements. Further, methods ofseparating a number of different inhalation anesthetics can be verycomplex due to differing chemistries and the potential for impurities,including by-products, in the combined materials.

Examples of anesthetics which can be captured are sold under thetrade-marks ETHRANE and FORANE, and are disclosed in U.S. Pat. Nos.3,469,011; 3,527,813; 3,535,388; and 3,535,425. The respective chemicalformulae for these anesthetics are: 1,1,2-trifluoro-2-chloroethyldifluoromethyl ether and 1-chloro-2,2,2-trifluoroethyl difluoromethylether. These chemicals are also commonly known as “enflurane” and“isoflurane”, respectively.

Other anesthetics of particular importance are sold under thetrade-marks SUPRANE and ULTANE, and are disclosed in U.S. Pat. Nos.3,897,502; 4,762,856; and 3,683,092. The respective chemical formulaefor these anesthetics are: 2,2,2-trifluoro-1-fluoroethyl-difluoromethylether and 2,2,2-trifluoro-1-[trifluoromethyl]ethyl fluoromethyl ether.These chemicals are commonly known as “desflurane” and “sevoflurane”,respectively. They are highly volatile organic compounds, produced in aliquid form and then evaporated and mixed with other carrier medicalgases, such as nitrous oxide, oxygen and/or medical air in theanesthetic gas machine before administered to a patient to be used as aninhalation anesthetic. The gas stream exiting the anesthetic gas machineis rich with inhalation anesthetics and contains entrained CO₂ andmoisture and possibly some by-products that potentially result from theanesthetic gas mix recirculation stream passing over soda lime absorbentin the patient breathing circuit.

While there may be methods and systems for adsorbing some of theseanesthetics individually or for purifying some of these chemicalsindividually to a level for medical use, effective methods and systemsof selective recovering anesthetics or a mixture of anesthetics from agas stream, for separating the anesthetics, if necessary, and forpurifying the anesthetics would be economically advantageous.

It is, therefore, desirable to provide a system and method for at leastsome of capturing, recovering, retrieving, separating and purifying avariety of inhalation anesthetics such as desflurane and/or sevofluranefrom a gas stream that overcomes at least some of the problems withconventional systems. It would be similarly desirable to provide asystem and method for at least some of capturing, recovering, separatingand purifying halogenated hydrocarbons generally.

SUMMARY

In one aspect of the application, described in more detail below, thereis provided a process for the recovery of at least one halogenatedhydrocarbon from a gas stream, the process comprising: exposing the gasstream to an adsorbent with a lattice structure having pore diameterslarge enough to permit molecules of the at least one halogenatedhydrocarbon to enter and be adsorbed in internal cavities of theadsorbent lattice, the adsorbent having a pore lattice structure with anaverage pore opening of between about 5 and about 50 angstroms; removingfrom the gas stream the adsorbent containing the adsorbed at least onehalogenated hydrocarbon; and regenerating the adsorbent with a purge gasby exposing the adsorbent to the purge gas under conditions whichefficiently desorb the at least one adsorbed halogenated hydrocarbonfrom the adsorbent. In particular, the process is intended to operatewithout causing catalytic reaction; without adsorbate breakdown and withhigh yields.

In some cases, the average pore opening is between about 5 and about 10angstroms. In other cases, the average pore opening is between about 15and about 30 angstroms. The adsorbent can be a SiO₂ based organophilicmaterial having a SiO₂ content of 90 wt % or greater. The adsorbent canbe less than 10% by weight of Al₂O₃. The adsorbent can be substantiallyfree of Al₂O₃. The adsorbent can have a weight ratio of SiO₂:Al₂O₃ of98:1 or greater. The adsorbent can have less than about 1% by mass ofcation. The adsorbent can have a neutral surface. The adsorbent can havea specific surface area of about 400 to about 1500 m²/g. The adsorbentcan have a specific surface area of about 500 to about 1250 m²/g. Theadsorbent can have a specific surface area of about 600 to about 900m²/g. The adsorbent can have average pore size of 20 angstroms, and/or asurface area of 750 m²/g.

During the process, the adsorbent can be exposed to the gas stream untilat least just prior to the adsorbent being saturated. In other cases theadsorbent can be exposed until after being saturated.

The at least one halogenated hydrocarbon can be removed from the purgegas by condensing the at least one halogenated hydrocarbon. The at leastone halogenated hydrocarbon can be an inhalation anesthetic. Theanesthetic can be sevoflurane, desflurane, halothane, isoflurane orenflurane. The at least one halogenated hydrocarbon can be abromochlorofluoro ether, a fluorinated alkyl ether, achlorofluorocarbon, a chlorofluoro ether, or one of their derivatives.

The gas stream can be a gas stream exiting an anesthetic gas machine, agas stream of a patient breathing circuit within an anesthetic gasmachine, or a gas stream associated with a hospital's central collectionsystem for the hospital's anesthetic gas machines' exhaust streams. Theanesthetics in the gas stream can be selectively adsorbed on theadsorbent material; and the anesthetics adsorbed on the adsorbentmaterial can be desorbed from the adsorbent material, condensed,separated and each purified to medical standards.

Exposing the gas stream to the adsorbent can comprise passing the gasstream through a bed of the adsorbent contained in a canister. Exposingthe gas stream to the adsorbent can comprise passing the gas streamthrough a bed of the adsorbent contained in a central collector or acanister, which is capable of adsorbing halogenated hydrocarbons frommultiple gas streams, such as the gas stream from the hospital centralanesthetic gas machines' gas disposal pipe.

The process can further comprise: detecting the at least one halogenatedhydrocarbon exiting the bed of adsorbent, actuating a detectable alarmto indicate that the bed of adsorbent is saturated, and replacing thesaturated adsorbent with unsaturated adsorbent. The saturated adsorbentcan be heated to an elevated temperature at controlled processconditions during regeneration of the adsorbent to assist in desorptionof the at least one halogenated hydrocarbon from the adsorbent. Thesaturated adsorbent can be heated with microwaves. A purge gas can beheated prior to being fed through or passed through the saturatedadsorbent to raise the temperature of the saturated adsorbent to theelevated temperature. The elevated temperature can be in the range of30° C. to 220° C. In some cases, the elevated temperature can be between30° C. and 180° C. The purge gas can be heated to a temperature in therange of 30° C. to 220° C. In some cases, the purge gas can be heated toa temperature between 30° C. and 180° C. The purge gas can be an inertgas such as nitrogen.

The at least one halogenated hydrocarbon can be a mixture of at leasttwo different anesthetics, the adsorbent can be configured to adsorb theat least two different anesthetics, the purge gas can desorb the atleast two different anesthetics from the adsorbent into the purge gas,and where the process can further comprise: condensing the two differentanesthetics desorbed into the purge stream into liquid form, andpurifying the condensed liquid form of the two different anesthetics byfractional distillation to isolate and separate purified, anesthetics.The fractional distillation can be performed under either vacuum orpressure. The process can further comprise washing the condensed liquidthat is a mixture of different anesthetics with water beforepurification by fractional distillation.

The mixture of the at least two different anesthetics purified byfractional distillation can comprise2,2,2-trifluoro-1-fluoroethyl-difluoromethyl ether and2,2,2-trifluoro-1-[trifluoromethyl]ethyl fluoromethyl ether.

In a further aspect, there is provided a use of an adsorbent having apore lattice structure with an average pore opening between about 5 andabout 50 angstroms for the adsorption of an inhalation anesthetic. Theinhalation anesthetic can be2,2,2-trifluoro-1-fluoroethyl-difluoromethyl ether or2,2,2-trifluoro-1-[trifluoromethyl]ethyl fluoromethyl ether. In somecases, the average pore opening is between about 5 and about 10angstroms. In other cases, the average pore opening is between about 15and about 30 angstroms. The adsorbent can be a SiO₂ based organophilicmaterial having a SiO₂ content of 90 wt % or greater. The adsorbent canhave less than 10% by weight of Al₂O₃. The adsorbent can besubstantially free of Al₂O₃. The adsorbent can have a weight ratio ofSiO₂:Al₂O₃ of 98:1 or greater. The adsorbent can have less than about 1%by mass of cation. The adsorbent can have a neutral surface. Theadsorbent can have a specific surface area of about 400 to about 1500m²/g. The adsorbent can have a specific surface area of about 500 toabout 1250 m²/g. The adsorbent can have a specific surface area of about600 to about 900 m²/g. The adsorbent can have average pore size of 20angstroms, and/or a surface area of 750 m²/g.

In a further aspect, there is provided an adsorbent for adsorbing ahalogenated hydrocarbon, the adsorbent having a pore lattice structurewith an average pore opening between about 5 and about 50 angstroms,less than 10% by weight of cation; and a surface area of between about400 m²/g and about 1500 m²/g. In some cases, the adsorbent has anaverage pore opening between about 5 and about 10 angstroms. In othercases, the average pore opening is between about 15 and about 30angstroms. The adsorbent can be a SiO₂ based organophilic materialhaving a SiO₂ content of 90 wt % or greater. The adsorbent can have lessthan 10% by weight of Al₂O₃. The adsorbent can be substantially free ofAl₂O₃. The adsorbent can have a weight ratio of SiO₂:Al₂O₃ of 98:1 orgreater. The adsorbent can have less than about 1% by mass of cation.The adsorbent can have a neutral surface. The adsorbent can have aspecific surface area of about 400 to about 1500 m²/g. The adsorbent canhave a specific surface area of about 500 to about 1250 m²/g. Theadsorbent can have a specific surface area of about 600 to about 900m²/g. The adsorbent can have average pore size of 20 angstroms, and/or asurface area of 750 m²/g.

In a further aspect, there is provided an adsorbent system for adsorbinghalogenated hydrocarbons, the adsorbent system comprising: one adsorbenthaving a pore lattice structure with an average pore opening of betweenabout 5 angstroms and about 10 angstroms; less than 10% w/w of Al₂O₃, asurface area of between about 400 m²/g and about 1500 m²/g; and anotheradsorbent having a pore lattice structure with an average pore openingof between about 15 angstroms and about 30 angstroms; less than 10% w/wAl₂O₃, surface area of between about 400 m²/g and 1500 m²/g.

In a further aspect, there is provided a sensor for detecting thepresence of halogenated hydrocarbons in a gas stream, the sensorcomprising: an electrical current generator for passing a currentthrough the gas stream; a conductivity sensor for determining thethermal conductivity of the gas stream based on the current passingthrough the gas stream; a processor for comparing the thermalconductivity with predetermined values to determine if halogenatedhydrocarbons are present in the gas stream.

In a further aspect, there is provided an adsorbent system for adsorbinganesthetics, the adsorbent system comprising: an input for receiving agas stream containing the anesthetics from an operating room exhaust orthe hospital central anesthetic gas exhaust; a non-chemical dryerconnected to the input; a chemical dryer connected to the non-chemicaldryer; a filter connected to the chemical dryer for removing bacterialand particulate matter; and an adsorber unit connected to the filter foradsorbing the anesthetics from the gas stream.

DESCRIPTION OF THE FIGURES

Other aspects and features of the present application will becomeapparent to those ordinarily skilled in the art upon review of thefollowing description of specific embodiments in conjunction with theaccompanying figures.

Embodiments will now be described, by way of example only, withreference to the attached Figures, wherein:

FIG. 1 is a schematic of a system for capturing anesthetics from a gasstream exiting an anesthetic gas machine;

FIG. 2 is a schematic of a system for capturing anesthetics from a gasstream within a patient breathing circuit of an anesthetic gas machine;

FIG. 3 is a schematic of a central collection system for capturinganesthetics from multiple anesthetic gas machines or a hospital centralanesthetic gas exhaust.

FIGS. 4a-c are schematics of contemplated embodiments of the centralcollection system;

FIG. 4d is a schematic of a contemplated “layered” canister with twoadsorbent layers;

FIG. 5 is a schematic of a system used to regenerate the adsorbedmaterial in a canister and recover the captured material;

FIG. 6a is a schematic of a single column, batch distillation apparatusfor purifying the components of the captured material;

FIG. 6b is a schematic of a multi-column, batch distillation apparatusfor purifying the components of the captured material;

FIG. 7 illustrates the mass change over time of a canister and a trap,each filled with an adsorbent and having desflurane passed therethrough;

FIG. 8 illustrates the mass change over time of a canister and a trap,each filled with an adsorbent and having sevoflurane passedtherethrough;

FIG. 9 illustrates the mass change over time of a canister and a trap,each filled with two adsorbents and having sevoflurane passedtherethrough.

DETAILED DESCRIPTION

Generally, the present application relates to methods and systems forcapturing a variety of halogenated hydrocarbons and for purifying thecaptured compounds. Compounds generally known as halogenatedhydrocarbons include bromo-, chloro- and/or fluoro-ethers, fluorinatedalkyl ethers, chloro-fluorohydrocarbons, chlorofluoroethers and theirderivatives.

Inhalation anesthetics are well known types of halogenated hydrocarbonswhich include isoflurane (Forane™), enflurane (Enthrane™), halothane(Halothane™) methoxyflurane (Penthrane™), desflurane (Suprane™) andsevoflurane (Ultane™).

Other well known halogenated hydrocarbons include the variety ofrefridgerant gases, such as Freons™ (which includetrichlorofluromethane, and dichlorodifluoromethane). This family ofhalogenated hydrocarbon compounds includes, for example, an alkyl groupor ether group substituted with one or more of chloro-, fluoro- andbromo-groups.

While the following description relates to the recovery of variousinhalation anesthetics, it is appreciated that the principles of theapplication, which are demonstrated by the following embodiments, can beequally applicable to the recovery of other types of halogenatedhydrocarbons.

During surgery, a patient is treated with inhalation anesthetics by wayof an anesthetic gas machine. It is appreciated that the use of the term“patient” is in a general sense and should not be limited to humanpatients. It is understood that anesthesia is practiced on a variety ofmammals, not only humans, but also animals such as horses, cattle andother forms of livestock, domestic pets and the like.

The inhalation anesthetics are first partly evaporated in the vaporizerof the anesthetic gas machine and typically delivered in combinationwith “medical air”, which is typically a combination of oxygen and/ornitrous oxide and/or air. As the patient breathes the gas streamcontaining the anesthetic (with support of a respirator), a desireddegree of unconsciousness is achieved and monitored by the anesthetist.Typically, not all of the anesthetic is adsorbed or metabolized by thepatient. Flow rates of the gas stream to the patient may be in the rangeof 0.5 to 7 liters per minute, where the concentration by volume of theanesthetic may be in the range of 0% to 8.5% depending on numerousfactors and conditions evaluated and monitored by the anesthetist.

It is important to ensure that the gas mixture containing anestheticbeing administered by the anesthetic gas machine is not exhausted intothe operating theatre, because exposure to the anesthetics can have bothshort term and long term effects on the people in the operating room. Assuch, scavenging systems are typically provided to contain theanesthetic rich gases (which may include patient exhalent) and/orexternally divert the anesthetic rich gases outside of the operatingroom. In the present embodiments, the anesthetic rich gas is adsorbed onan adsorbent before the gas is vented to the atmosphere.

In one embodiment of a collection system herein, the collection may beperformed using an container collection system. A container collectionsystem is understood to be a collection system where one or morecanisters are used to collect anesthetics from a single anesthetic gasmachine or from multiple anesthetic gas machines. One embodiment of acontainer collection system is illustrated in FIG. 1 where a singlecanister is in line with the outlet of the anesthetic gas machine. Inthis system the patient represented at 10 is connected to a mask (notshown) having a gas line 14 communicating therewith. The desired mixtureof anesthetic and carrier gas or gases is delivered in gas line 14 tothe patient 10. The anesthetic rich gas is returned in exhalent line 16to the anesthetic gas machine 18. The anesthetic gas machine 18, whichis supplied with an anesthetic and carrier gases (for example medicalair—in this example, oxygen and air) in oxygen line 20, anesthetic line22 and air line 24, is operated to introduce the desired mixture in gasline 14. The anesthetic rich gas in exhalent line 16 is discharged fromthe anesthetic gas machine 18 via discharge line 26. A canister 28,having an inlet line 30 and an outlet line 32, is interposed indischarge line 26 at a position outside of a patient breathing circuit.The anesthetic rich gas in discharge line 26, therefore, flows throughthe canister 28 before ultimately exhausting to atmosphere 34. With someanesthetic gas machines, the patient breathing circuit can be open,semiclosed or closed. An open circuit results in no rebreathing by thepatient of the gas returned to the anesthetic gas machine via exhalentline 16. A semiclosed circuit results in partial rebreathing by thepatient of the gas returned to the anesthetic gas machine via exhalentline 16. A closed circuit results in complete rebreathing by the patientof the gas returned to the anesthetic gas machine via exhalent line 16.Anesthetic gas machines with semiclosed or closed circuits can use a CO₂absorber to scrub the patient's exhaled carbon dioxide.

The canister 28 is charged with an adsorbent that adsorbs the anestheticfrom the gas stream exiting the anesthetic gas machine, intending toleave the stream discharge to atmosphere 34 substantially free ofinhalation anesthetic. An anesthetic sensor 36 may be provided inexhaust line 38 to sense the presence of anesthetics exiting from thecanister 28. It is appreciated that an adsorption front of adsorbedanesthetics travels along the bed of adsorbent towards the canisteroutlet as the anesthetic is adsorbed. Such an adsorption front willusually have a curved profile across the canister as it approaches theoutlet. The sensor would sense when any portion of the adsorption fronthas broken through the adsorbent into the outlet. Replacement of thecanister may be desirable at this time even though the bed of adsorbentmay not be fully saturated with anesthetic. The anesthetic sensor 36 maybe connected via a signal line 40 to the anesthetic gas machine 18, orto some remote monitoring station (not shown). The anesthetic gasmachine 18 or remote monitoring station may be equipped with an alarm 42which is actuated when the anesthetic sensor 36 senses anesthetics inexhaust line 38. The alarm can be a light and/or audible alarm. Thiswould indicate to the anesthetist or a technician that the canister 28should be replaced so that continued recovery of anesthetics isachieved. It is appreciated that a bypass 44 controlled by a bypassvalve 46 may be provided to route the gas stream exiting the anestheticgas machine 18 past the canister 28 during replacement of the canister.In this instance, a shut-off valve 48 is provided in discharge line 26to shut off the supply to canister 28 during replacement of thecanister. Instead of bypass 44 and shut-off valve 48, a three-port valvecould direct the flow of gas past the canister 28 during replacement ofthe canister.

There may be cases where the medical air supply may be left on eventhough no anesthetic is being used. In such a situation, it isundesirable to continue to flow medical air through the canister sincethe continuous flow of medical air can slowly desorb the anestheticspreviously captured. In order to address such a situation, a secondanesthetic sensor 50 may be provided in discharge line 26 in order todetect anesthetics. In the event that no anesthetics in the flow aredetected by the anesthetic sensor 50, bypass 44, controlled by bypassvalve 46, could be triggered to route the medical air directly to theatmosphere at 34.

As discussed above, anesthetic gas machines can include partially closedor closed breathing circuits. In such breathing circuits, patientexhalent is circulated through the breathing circuit via a ventilatorand is scrubbed to remove exhaled carbon dioxide before beingre-breathed by the patient. In an alternative collection system, termedan “breathing circuit collection system”, the anesthetics are adsorbedby a canister in-line with the breathing circuit. The canister of thisembodiment is positioned to adsorb anesthetic gas before the anestheticgas machine discharges the exhaust gas to atmosphere.

As illustrated in FIG. 2, the anesthetic gas machine 18 accepts ananesthetic and carrier gases (for example medical air—in this example,oxygen and air) in oxygen line 20, anesthetic line 22 and air line 24.These are mixed in mixer 51 a. The anesthetic rich gas is delivered topatient 10 via gas line 14. Patient exhalent is returned to theanesthetic gas machine 18 via patient exhalent line 16. The returned gasis delivered to ventilator 51 b via ventilator line 51 c. The anestheticrich gas is delivered to carbon dioxide scrubber 51 d via scrubber line51 e and scrubbed of carbon dioxide. The scrubbed gas is delivered tocanister 28 via canister inlet line 30. The canister 28 is charged withan adsorbent that adsorbs the anesthetic from the gas stream exiting thecarbon dioxide scrubber 51 d.

Although FIG. 2 illustrates the canister 28 as being positioned afterthe ventilator 51 b and scrubber 51 d, it should be understood that therelative positions of the ventilator, scrubber and canister along thebreathing circuit could be changed.

The gas flowing out of canister outlet 32 is directed via a circulationvalve 51 f either back to the mixer 51 a or, via discharge line 26, outof the anesthetic gas machine 18 and ultimately to atmosphere 34. Ananesthetic sensor 36 may be provided in discharge line 26 to sense thepresence of anesthetics exiting the anesthetic gas machine 18. Sensorsand valves, such as those described above with regard to the containercollection system, could be used to determine when the canister needs tobe replaced and to direct the flow of gas around the canister duringreplacement of the canister.

In an alternative system, illustrated in FIG. 3, the anesthetics arecaptured by a central adsorber collection system 52. A central adsorbercollection system is understood to be a collection system that takes asits input anesthetics from multiple anesthetic gas machines (e.g. 18′,18″ and 18′″), which may be located in multiple operating rooms. Thiscentral collection system would operate in a similar fashion to thecontainer collection system described above, in that the centraladsorber collection system would be charged with at least one adsorbentwhich selectively adsorbs the anesthetics from the combined gas streamsexiting the anesthetic gas machines, intending to leave the dischargestream substantially free of anesthetics for ultimately exhausting toatmosphere 34. The central adsorber collection system may includeseveral adsorbers and each geometrically sized to facilitate largervolume of adsorbate in the system and/or less frequent replacementsand/or desired longer adsorption time.

An anesthetic sensor 36′ may be provided in the central adsorbercollection system exhaust line 38′ to sense the presence of anestheticsexiting the central adsorber collection system. The anesthetic sensor36′ would sense when anesthetics have broken through the adsorbent intothe exhaust and prompt a user with feedback (e.g. an alarm) to changethe adsorbent by, for instance, replacing one or more adsorbers,replacing the adsorbent in one or more adsorbers, or regenerating theadsorbent. Trap 54 may be provided in the exhaust line 38′, locatedbefore the system exhausts to the atmosphere 34, in order to reduce thepossibility that anesthetics are released to the atmosphere. The trap 54may have the same adsorbent as the central adsorber collector, or mayhave a different adsorbent, such as activated carbon, silicalite, ormolecular sieves.

An alternative to providing the anesthetic sensor 36′ for sensing ananesthetic in the exhaust line is to provide a weight sensor (e.g. aload cell) such that the weight of the capture device (or adsorbent orcanisters) could be monitored and the user could be prompted to changeor regenerate the adsorbent once a predetermined weight of anestheticwas collected in the central adsorber collection system.

In another alternative to using the anesthetic sensor 36′, historicalloading patterns could be used to determine an appropriate time tochange or regenerate the adsorbent or to determine an appropriateadsorber size to support a given time of collection. Replacement orregeneration of the adsorbent in any of the above alternatives may bedesirable even though the adsorbent is not fully saturated withanesthetic.

Sensors 56′, 56″ and 56′″ may be provided in central adsorber collectionsystem inlet lines 26′, 26″ and 26′″. The sensor 56′, 56″ and 56′″ sensethe presence of anesthetics in the medical air and/or operation of theanesthetic gas machine. In cases where no anesthetics are detected, orif the associated anesthetic gas machine is not in operation, inletlines 26′, 26″ and/or 26′″ may be closed off to isolate the appropriateoperating room from the central adsorber collection system 52. The inletlines 26′, 26″ and 26′″ may alternatively be used to route the medicalair, via bypass 58, to the atmosphere and away from the centralcollection system 52. Closing off the inlet lines 26′, 26″ and 26′″ orrouting the medical air through bypass 58 can be achieved using bypassvalves 59′, 59″ and 59′″.

One example of such a sensor is a sensor which can be used to detectanesthetics in the exhaust line. Such a sensor could measure thermalconductivity of the gas in the exhaust line and transform the thermalvariations into an electrical signal. Thermal conductivity of the gasstream with anesthetic is a physical property found to vary under normaloperating conditions of the anesthetic gas machine. Such a signal couldbe used to provide a numerical indication of the concentration ofanesthetic in the exhaust line. As described above, the signal couldalso be used to operate a valve to isolate the operating room or toroute the medical air to the atmosphere. Another example of anappropriate sensor would be a pressure sensor or valve which woulddetect pressure coming from the anesthetic gas machine.

One of the issues involved in a central adsorber collection systemrelates to the flow rate and concentration of anesthetics in the flow.Typically, a hospital scavenging system uses a pump or blower device 60located before the central collection system to draw the gas stream fromvarious operating rooms into the scavenging system. This device drawsthe gas stream originating from the anesthetic gas machines 18′, 18″ and18′″, as well as additional “make up” air. An increased flow rate due tothe make up air results in a dilution of the concentration ofanesthetics 22′, 22″ and 22′″. This dilution can be, for example, in therange of 1:20 (volume of anesthetic gas stream from the anesthetic gasmachine:volume of flow entering the hospital scavenging system andpassing through the central collection system) since the flow rate froman anesthetic gas machine can be about 2 L/min, while the flow rateentering the hospital scavenging system can be 40 L/min. Given thedilution of anesthetics passing through the central collection system,the capture device (e.g. each canister of the central collection systemspecifically, or the central collection system in general) should bedesigned to ensure that the residence time is adequate for the adsorbentmaterial to adsorb the anesthetics. Changing the residence time can beeffected by changing the volume of the capture device or by changing theflow rate of the gas. It is appreciated that the relationship betweenthese variables is given by the equation: Residence Time=Capture DeviceVolume/Gas Flow Rate.

FIGS. 4a, 4b and 4c show alternative embodiments for canisters making upthe collection systems described above. FIG. 4d shows one embodiment ofthe components which could be included in a canister. The collectionsystem may be made up of a single canister of adsorbent (FIG. 4a ), ormay have multiple canisters of the same or various types of adsorbents.Canisters may be of the same or different sizes or capacities. Themultiple canisters of adsorbent may be in series (FIG. 4b ) or inparallel (FIG. 4c ). With multiple canisters in parallel, the collectionsystem may first pass the input gas through one or more canisters untilthe adsorbent in that canister (or canisters) is saturated, and thenpass the input gas through another canister or set of canisters. Thiscould be achieved by including anesthetic sensors 62 and 62′ in theexhaust line of each canister to detect when anesthetic gases havebroken through the adsorbent of that canister into the exhaust, andbypasses controlled by bypass valves 64 and 64′ to route the input gasaround that canister. Alternatively, the collection system could routethe input gas away from a canister when the canister reaches apredetermined weight. In another embodiment, the collection systems maypass the input gas through all the parallel canisters at the same time.

In various cases, the canisters making up a collection system mayinclude different adsorbent materials, and may be of differentgeometrical configurations, different weights and volumes, differentmaterials of construction, and have different capacities for adsorption.The specific variables can be chosen in view of the variableconcentrations of the anesthetic gas in the administered gas mixture;the variable flow rates of the administered gas mixtures; the variousscavenging systems commonly used in hospitals (active or passive); thevarious anesthetic gas machine exhausts; the different anesthetic gasmachine type of outlets; and other operating room settings. Theconfigurations of the canisters for a particular application can beadapted to meet a hospital's requirements for the frequency of adsorberreplacement, space requirements, or various other factors.

In each case, the canister can be configured to facilitate adsorbentloading and unloading, to provide proper connection to the anestheticgas exhaust outlet; to ensure gas stream flow distribution duringadsorption and regeneration; to provide easy handling; and toaccommodate space availability.

A canister, a canister collection system, or a central adsorbercollection system may be filled with more than one adsorbent. In such asituation, the different multiple adsorbents may be layered in separate“beds” within the single canister, as illustrated in FIG. 4d where 66identifies a first bed, 68 identifies a second bed and 70 identifies amesh which keeps the beds separate but allows the gas to flow from theinlet end of the canister to the outlet end of the canister. Thecanister illustrated in FIG. 4d also shows a diffuser 71 at the inletend, which distributes gas throughout the canister thereby reducing thepossibility that there are pockets of adsorbent which do not contact thegas stream.

Such a layered system could be used in a “staged” adsorption where theobjective of each layer is to adsorb a specific target compound orcompounds (e.g. the objective of the first layer would be to adsorbwater, the objective of the second layer would be to selectively adsorbdesflurane and isoflurane, and the objective of the third layer would beto adsorb sevoflurane). Such a layered bed could be removable from thecanister for separate regeneration of the multiple adsorbents. It isappreciated that such a layered canister could be used in both thecentral collection system described above, as well as the containercollection system described previously.

In one embodiment of a “staged” adsorption canister, the first layercontacted by the mixture of anesthetics could be a layer of adsorbenthaving an average pore diameter of between about 5 angstroms and about10 angstroms. This first adsorbent would adsorb one or more anesthetics,while not adsorbing other anesthetics.

The second layer contacted by the anesthetics could be a layer ofadsorbent having an average pore diameter of between about 15 angstromsand about 30 angstroms. This second adsorbent would adsorb one or moreanesthetics, including, for example, sevoflurane. In such an embodimentof a “staged” adsorption canister, adsorption of a mixture of desfluraneand sevoflurane could result in preferential adsorption of desflurane onthe first layer and preferential adsorption of sevoflurane on the secondlayer.

The collection systems may have one or more in-line filter (not shown)to remove particulates and/or biological contamination before thecontamination reaches the central collector. The filter can be a 0.2micron, hydrophobic, gas cartridge filter. An example of such a filteris the High Flow TETPOR™ II pharmaceutical grade gas cartridge filtermade by Domnick Hunter Limited, England.

It may be advantageous to remove specific targeted compounds from thegas flow using one or more selective adsorbents before the gas flowpasses through the central collection system or container collectionsystem. Moisture can be removed using a condenser (not shown) and/or maybe removed using 3A, 4A, or other known conventional desiccants (notshown) having appropriately sized pores to avoid adsorbing theanesthetics. In order to prevent or reduce decomposition of ananesthetic caused by the desiccant, it may be desirable to first removemoisture using a condenser and then appropriately limit the amount ofdesiccant used to dry the gas flow and/or select a desiccant which doesnot result in decomposition of the anesthetic. The desiccant may beseparated from the adsorbent used to adsorb the anesthetics, with thedesiccant and adsorbent being located in separate canisters.

With regard to the decreased adsorption capacity of the material in thepresence of water, Table 1, below, shows the breakthrough and maximumcapacity of two particular halogenated anesthetics (sevoflurane anddesflurane) on an adsorbent with and without water. The adsorbents wereplaced in lab-sized canisters, having a capacity of about 1 kg ofadsorbent, which are smaller than commercially sized canisters.Breakthrough capacity of water was 127 g and the maximum capacity ofwater was 322 g. As can be seen, breakthrough capacities and maximumcapacities of both sevoflurane and desflurane are significantly reducedin the presence of water.

TABLE 1 Breakthrough capacity (g) Maximum Capacity (g) SevofluraneDesflurane Sevoflurane Desflurane w/out w/out w/out w/out w/ H₂O H₂O w/H₂O H₂O w/ H₂O H₂O w/ H₂O H₂O 188 378 113 234 300 542 210 369

According to one embodiment herein, the canister is charged with anadsorbent material having an organophillic pore lattice structure. Theadsorbent can be based on SiO₂-based molecular sieves. Molecular sievesshould be understood to be materials which contain tiny pores of arelatively precise and relatively uniform size. Materials used as anadsorbent for gases and liquids can include aluminosilicate minerals,clays, porous glasses, microporous charcoals, zeolites, active carbons,silical gel or synthetic materials.

The adsorbent can have an average pore opening of about 5 to about 50angstroms. In particular embodiments, the adsorbent can have an averagepore opening of about 5 to about 10 angstroms. In other embodiments, theadsorbent can have an average pore opening of about 15 to about 30angstroms. It has been found that adsorbent material with an averagepore size greater than 15 angstroms can be used to adsorb one or moreanesthetics. Anesthetics able to be adsorbed by an adsorbent having anaverage pore opening greater than 15 angstroms include sevoflurane anddesflurane.

Molecular sieves based on SiO₂ typically have a formula ofM_(x)(Al₂O₃)_(y)(SiO₂)_(z) where M is a cation. It is preferable toavoid adsorbent materials with a basic surface as some halogenatedhydrocarbons can be degraded under basic (i.e. high pH) conditions.Since Al₂O₃ is basic in character (typically existing as Al(OH)₄ ⁻ underneutral conditions), adsorbents contemplated in the present applicationpreferably have less than about 10% by total weight of Al₂O₃. Morepreferably, the adsorbent used in the present application has less than5% by total weight of Al₂O₃. An adsorbent which is substantially free ofAl₂O₃ is particularly preferable. It would be understood that anadsorbent which is “substantially free of Al₂O₃” is an adsorbent whichhas no more than about 1% w/w of Al₂O₃.

Adsorbent material with a neutral surface (i.e. with low levels ofcations in the lattice) is preferable, since cations (such as Na⁺, K⁺,Ca²⁺, Al³⁺ etc) may cause catalytic reactions and degradation of thehalogenated hydrocarbon being adsorbed. An adsorbent material with aneutral surface would be understood to mean an adsorbent having lessthan 1%, preferably less than 0.1% and particularly preferably less than0.01%, by mass, of cation.

It would be understood that changes in pore size and active surface areaof the material would affect the total amount of halogenated hydrocarbonwhich could be adsorbed. Adsorbent having a specific surface area ofabout 400 m²/g to about 1500 m²/g could be used. According to oneembodiment, the adsorbent is an amorphous silica adsorbent that has anaverage pore size of about 20 angstroms, a specific surface area ofabout 750 m²/g, a pore volume of about 0.4 mL/g and has less than about1.0 wt % Al₂O₃.

The canister can be charged with an additional adsorbent material thathas a pore lattice structure with an average pore opening of betweenabout 5 and about 10 angstroms. This additional adsorbent material canbe used to adsorb one or more anesthetics. One anesthetic which is ableto be adsorbed by the additional adsorbent material is desflurane. Usingthe additional adsorbent material would allow selective adsorption ofdesflurane from a mixture of desflurane and sevoflurane.

According to one embodiment, the additional adsorbent material is asilica adsorbent that has average pore size of about 6 angstroms, aspecific surface area of about 400 m²/g, a pore volume of about 0.14mL/g, and has less than about 1.0 wt % Al₂O₃.

In one embodiment, the canister, which may be cylindrical in shape, hasan inlet located at or near the bottom and an outlet at the other end.The inlet can be attached via a pipe to a diffuser at the bottom of thecanister, as illustrated in FIG. 4d . Alternatively, the inlet and anoutlet can both be located at the same end. The canister could be madefrom any material with appropriate heat resistant and corrosionresistant properties. The material could be, for example, ceramic,glass, engineered plastic or stainless steel, such as SS316.

The gas stream in discharge line 26 exiting the anesthetic gas machine18 (see FIG. 1) typically contains moisture. This has presentedsignificant problems in the past in attempting to recover anestheticsfrom gas stream exiting anesthetic gas machines. In order to overcomethis problem, the moist gas stream may be first passed through ahydroscopic adsorbent which adsorbs the moisture, but has pore sizesthat avoid the adsorption of anesthetic. In this manner, the moist gasstream can be dried prior to capture of the anesthetic on the adsorbent.It is would be readily understood that the hydroscopic adsorbent couldbe placed inside or outside the canister, as long as it was in-line withthe anesthetic adsorbent and adsorbed the moisture before the gas streampassed through the anesthetic adsorbent.

A single patient is usually treated with a single anesthetic. However,during the time that a container collection system or a breathingcircuit collection system is attached to an individual anesthetic gasmachine, several different operations may occur with differentanesthetics being used. Additionally, in a central adsorber collectionsystem, each anesthetic gas machine in each operating room of a hospitalmay be using different anesthetics. In either of the above situations, acanister of adsorbent in either of (i) a central adsorber collectionsystem or (ii) an canister collection system would be exposed to severalanesthetics, in sequence or simultaneously. Different anesthetics mayhave different effects on the anesthetic adsorbents. It is believed thatthe adsorption of an anesthetic results in heat generated during theadsorption process. It is therefore sometimes desirable to first captureone or more specific anesthetics using a first anesthetic adsorbentbefore capturing one or more other anesthetics. In a similar manner, itmay be desirable to remove as much water as possible before adsorbingthe inhalation anesthetic in order limit the heat released during theadsorption process.

Canisters loaded with adsorbed anesthetics can be subjected to a processto regenerate the anesthetic adsorbent in the canister 28 and to recoverthe anesthetic material. An embodiment of a general desorption system isillustrated in FIG. 5. A desorption system could process a singlecanister at a time or multiple canisters in series or in parallel. Adesorption system could be integrated with a central collection systemso that the adsorbent of the central collection system could beregenerated without having to be removed from the central collectionsystem.

In the system of FIG. 5, the canister may be heated within a desorptionvessel 72, to enhance the desorption of the adsorbed anesthetics. In oneexample, the adsorbents are heated to a temperature range of about 25°C. to about 220° C. Preferably, the desired temperature is between 60°C. and 120° C. It is appreciated that with different types ofhalogenated hydrocarbons, different temperature ranges may be necessaryto desorb the compounds. In order to heat the adsorbents within thecanister to the desired temperature, the desorption vessel 72 may be aconventional oven having heating coils surrounded by insulatingmaterial. It is understood that in view of the transparency of theanesthetic adsorbing material to microwaves, a microwave oven may besubstituted for the conventional oven.

While FIG. 5 shows one canister, it should be appreciated that thedesorption process could be run with more than one canister (not shown)connected in parallel or in series.

A purging gas is passed through the canister 28 to desorb the organicanesthetics from the adsorbent or adsorbents. In accordance with aparticular aspect of this application, the purging gas is an inert gas.The inert purging gas can be nitrogen. In one arrangement, the canisteror canisters are not contained within a heated desorption vessel 72(such as a conventional or microwave oven) but heat for desorbing theanesthetics can come from heated purging gas.

The purging gas may be heated using a heater 74. As noted above, in somecases, the adsorbents in canister 28 may be heated by heating thenitrogen gas or air purging stream, even if direct application of heatto the canister is not applied. In accordance with the embodimentillustrated in FIG. 4, nitrogen gas is heated in heater 74 to thedesired temperature in the range of about 25° C. to about 220° C.Preferably, the desired temperature is between about 60° C. and about120° C. FIG. 4 shows the desorption system as a closed loop, the purginggas being continuously recycled. Any loss of purging gas from the system(e.g. due to removal of material from the system) can be replenished viapurging gas source 76.

It may be desirable to desorb canister 28 at a higher temperature, forexample if removal of water is desired, typically after the anestheticshave already been desorbed. In such a situation, canister 28 and/or thepurging gas stream can be heated to about 200° C. or higher. It may evenbe desirable to heat the canister 28 and/or the purging gas stream to ashigh as 1000° C. in order to more thoroughly regenerate the canister.

It is appreciated that temperature and pressure both affect the amountof time required to regenerate the adsorbent. Increasing the temperatureand/or decreasing the pressure reduce the amount of time required fordesorption, while decreasing the temperature and/or increasing thepressure would increase the amount of time required for desorption.

In some situations, it may be desirable to desorb the canister under apartial vacuum since the reduced pressure would reduce the temperaturerequired to regenerate the adsorbent, and thereby reduce decompositionof any temperature sensitive adsorbed anesthetics. In an embodimentwhere the desorption process is operated under vacuum, the adsorbentsmay be heated to 50° C. to effect desorption of the anesthetics. In anembodiment at standard pressure, the adsorbents may be heated to about120° C. to effect desorption of the anesthetics. It is believed that ata reduced pressure, the canister 28 could be regenerated at temperaturesbetween about 50° C. and about 60° C. Regeneration of adsorbent couldalso be achieved at temperatures as low as 25° C., where the time forregeneration is thereby extended.

The purging gas passes through the adsorbents in the canister 28. Thepurging gas exits the canister 28 through purging gas exit line 78 andmay pass through a temperature sensor 80. The temperature sensor 80provides an indication of the temperature of the purging gas in the exitline 78. When the temperature of the purging gas in the exit line 78achieves a temperature nearing that of the temperature in purging gasentrance line 82, it can be determined that the adsorbents are at atemperature approximating the inlet temperature and that most of theanesthetics have been desorbed. The system is then run for a desiredperiod of time beyond that point to ensure complete desorption.Alternatively, the purging gas can be run for a predetermined time, withthe predetermined time being based on empirical knowledge gained fromhistorical desorption experiments. In another alternative, a sensor canbe used to determine the presence of anesthetic in the exit line.

The desorption process may be automated and a temperature sensor 84 maybe included in the inlet side to measure the temperature of the incomingstream. By way of a suitable microprocessor, the signals from thetemperature sensors 80 and 84 may be fed to a control system 86 whichcompares the temperatures and actuates a signal to indicate thatcanister regeneration process is complete. It is appreciated thatregeneration of the adsorbents may take place at lower temperaturesoutside of the preferred range.

It is appreciated that, adsorbents may be removed from their canisterand placed with adsorbents removed from other canisters. The combinedadsorbents may then be regenerated in a separate vessel in a manner asdiscussed above with respect to a single canister.

The stream of purging gas coming from the canister via the purging gasexit line 78 can optionally be passed through an aqueous condenser 90 toremove water from the gas stream. This aqueous condenser 90 can beoperated at a temperature of, for example, 0° C. to 20° C. The gasstream can then be optionally passed through a desiccant dryer 92 toremove any residual water. The desiccant dryer 92 could, preferably,remove sufficient moisture to lower the dew point to below about −60° C.The moisture content (i.e. dew point) could be measured, for example,with moisture sensor 93. The dessicant dryer 92 could include multiplecontainers of dessicant and the gas stream could be directed through thecontainers in series and/or in parallel, in a similar manner asdiscussed with regard to the canisters of adsorbent illustrated in FIG.4a -c.

The gas stream can also be passed through a microfilter 94 to remove anyparticulates and/or biological contamination. In one embodiment, thefilter is a 0.2 micron, hydrophobic, gas cartridge filter. An example ofsuch a filter is the High Flow TETPOR™ II pharmaceutical grade gascartridge filter made by Domnick Hunter Limited, England. Finally, thegas stream can be passed through hydrocarbon condenser 96. The purposeof the hydrocarbon condenser 96 is to remove, in liquid form, theanesthetic from the purge gas. The hydrocarbon condenser 96 can becooled with an appropriate coolant (such as liquid nitrogen, siliconeoil cooled by dry ice, or gaseous nitrogen at cryogenic temperature),which can be fed through the hydrocarbon condenser 96 via coolant inlet98 and coolant exit 100. This provides sufficiently cool temperatures inthe hydrocarbon condenser 96 to cause the anesthetics to condense andcollect, via connection line 102, in vessel 104 as halogenatedcondensate 106. The hydrocarbon condenser 96 can be operated at acondensing temperature between about −20 and about −100° C. Inparticular embodiments, the hydrocarbon condenser 96 can be operated ata condensing temperature between −20 and −65° C. The gas stream can berecycled to the heater 74 via recycle line 108. A sensor capable ofdetecting anesthetic could also be used to adjust the conditions at thehydrocarbon condenser 96.

It would be appreciated that any of the noted elements (e.g. desiccant92, microfilter 94 or the like) could be doubled, tripled, quadrupled,or otherwise and could be attached in serial or in parallel as a way ofintroducing redundancy and continuous operation into the system. In thesituation where elements are arranged in parallel it may be advantageousto include a sensor or timer to shift between parallel streams. Forexample, where there are multiple desiccant dryers 92, it may beadvantageous to also include a moisture sensor 93 which could detectmoisture in the gas stream exiting the first desiccant dryer 92 andswitch the gas stream to a second desiccant dryer arranged in parallel.One example of moisture sensor 93 is a dew point monitor.

As discussed above, a mixture of anesthetics may be adsorbed by theanesthetic adsorbing material. Hence, the halogenated condensatecollected from the desorption process may consist of a mixture ofanesthetics and may also include additional decomposition products andother compounds or impurities. Regardless of the composition of thehalogenated condensate, the individual anesthetics are preferablyseparated, isolated and purified to predetermined standards, which mayinclude medical standards at which the recovered anesthetics can beadministered to patients. The medical standards for each anesthetic havea regulated purity level, normally in excess of 95 wt %, with theremaining impurities also having specified limits. An alternativepredetermined standard may be to provide a level of purity that couldthen conveniently be subject to additional processing to reach themedical standard. For example, the anesthetics could be provided in aform suitable to be a raw material for subsequent processing.

To achieve the desired purity, the halogenated condensate can besubjected to fractional distillation. It is understood that it would bepossible to operate a distillation process as either a batch orcontinuous process. It is appreciated that a single column ofappropriate length could be used to purify all the anesthetics, or thata multi-column system could be used. It is also appreciated thatdistillation could be used to purify only a single anesthetic (such asdesflurane, sevoflurane or isoflurane) while leaving the remaininganesthetics in the halogenated condensate. In this manner, thehalogenated condensate could be enriched with one or more of theanesthetics.

An embodiment of a distillation system with a single column, used for abatch process, is illustrated in FIG. 6a . Halogenated condensate isheated in reboiler 108 and fed to column 110. The vapors in column 110are condensed in condenser 112. A vacuum system 114 at the top of thecolumn 110 could allow the distillation process to be performed under apartial vacuum. The condensed liquid exiting the condenser 112 is splitinto two streams: collection stream 116, which is purified liquidcollected in collector 118; and return stream 120, which is a streamthat re-enters the distillation column 110. The ratio between thecollection stream 116 and the return stream 120 is termed the “refluxratio”. A properly chosen reflux ratio aids in achieving the desiredpurity.

The distillation system illustrated in FIG. 6a could also include one ormore testing points along the column, such as via testing ports 122 and124, which could be used to test the temperature and composition of thevapors in the column during distillation. The temperature and/or thecomposition of the vapors could be used to set the reflux ratio and/orthe amount of energy used to heat the reboiler 108.

Another system is a multi-column, batch distillation system, an exampleof which is illustrated in FIG. 6b . This system consists of amultistage fractional distillation system having three distillationcolumns 110 a, 110 b and 110 c. The halogenated condensate is heated inreboiler 108 a and rises into column 110 a. Sufficient energy is appliedto reboiler 108 a to cause the liquid to boil and provide a vaportake-off in vapor take-off line 112 a. The vapor in line 112 a is fed tothe bottom of column 110 b. Condensate from the bottom of the column 110b is fed back into the top of column 110 a via condensate return line114 a. In a similar manner, the vapor in vapor take-off line 112 b isfed to the bottom of column 110 c. Condensate from the bottom of column110 c is fed back into the top of column 110 b via condensate returnline 114 b. The vapor in vapor take-off line 112 c can be condensed incondenser 122. A vacuum system 124 at the top of the distillation column110 c can allow the distillation process to be performed under a partialvacuum. The condensed liquid exiting the condenser 122 is split into twostreams: collection stream 126, which is a purified liquid collected incollector 128; and return stream 130, which is a stream that re-entersthe distillation column 110 c. As discussed above, the ratio betweencollection stream 126 and the return stream 130 is termed the “refluxratio”. A properly chosen reflux ratio aids in achieving the desiredpurity.

It will be appreciated that any of the contemplated distillation systemsmay be operated at atmospheric pressure or under a partial vacuum orunder pressure. Additionally, the contemplated distillation systemscould have in-line analysis capability to determine the temperature andcomposition of the liquid and/or vapor phase at any point along thecolumn. This in-line analysis capability could be connected to acomputer controlled automatic feedback system which could control theamount of heat applied to the reboiler, the pressure in the column,and/or the reflux ratio in order to regulate the distillation process.

The contemplated distillation columns may be packed with an appropriatepacking to increase the internal surface area of the column and increasethe number of theoretical plates per unit length of column. Examples ofan appropriate packing material could include metal, ceramic or glass.

The reboiler of the contemplated batch distillation systems may beoperated at a first setting in order to process a first component of amixture before being operated at a second setting in order to process asecond component of the mixture. The reboiler(s) may be operated betweenabout 500 kW and about 1500 kW, but the actual setting is a function ofthe quantity and composition of the material in the reboiler, including,for example, the reflux ratio.

In one particular embodiment of a multi-column, batch distillationsystem used for proof of concept and interim processing, distillationcolumn 1 can be 190″ in length and 3″ in outside diameter. Distillationcolumn 2 can be 202″ in length and 3″ in outside diameter. Distillationcolumn 3 can be 166″ in length and 3″ in outside diameter. In anotherparticular embodiment, distillation column 1 can be 166″ in length and3″ in outside diameter. Distillation column 2 can be 176″ in length and3″ in outside diameter. Distillation column 3 can be 115″ in length and3″ in outside diameter. The packing material in the columns can be a0.24 inch protruded metal ribbon, with a surface area of 372 square feetper cubic foot. Such a packing material can have a packing factor of420. One example of such a packing material is 0.24-Inch Pro-PakProtruded Packing.

Within a mixture of anesthetics, a number of impurities can also bepresent. These impurities may include chloromethane;2,2,2-trifluroethanol; chloromethyl 2,2,2-trifluoromethyl-ethyl ether;1,1,1,3,3,3-hexafluoroisopropanol; [(CF₃)₂CHO]₂═CH₂; and/or(CF₃)₂CHOCH₂OCH₂CF₃. Such impurities may result in azeotropic mixtureswith one or more of the anesthetics, resulting in reduced effectiveyields during distillation. In a situation where impurities are present,it may be desirable to reduce the amount of or remove the impuritiesfrom the halogenated condensate before distillation is performed. As oneexample, the halogenated condensate may be washed with water, preferablyin about a 1:2 wt/wt ratio. The water washing may be repeated untildesired specifications (for example, a desired reduction in the amountof impurities) are met. In the situation where1,1,1,3,3,3-hexafluoroisopropanol is present, it may be desirable towash with water until the level of 1,1,1,3,3,3-hexafluoroisopropanol isless than about 1.5% wt/wt, and preferably less than 0.1% wt/wt. Thelevel of 1,1,1,3,3,3-hexafluoroisopropanol may be analyzed by gaschromatography or other suitable analytical technique.

Without limiting the scope of the present application, the followingexamples exemplify aspects of and information relating to theembodiments herein. The following examples were performed in laboratorysituations using experimental canisters. It will be understood that theexperimental canisters may be smaller than commercially sized canisters.

Example 1

The breakthrough and maximum adsorption capacities of an adsorbent wasdetermined for desflurane and sevoflurane. A canister was filled withabout 1,100 grams of an adsorbent. The adsorbent was an amorphous silicaadsorbent with an average pore size of about 20 angstroms, a specificsurface area of about 750 m²/g, and less than about 1.0 wt % Al₂O₃.Desflurane at a concentration of 6% by volume, in nitrogen was passedthrough the canister at a rate of 2 liters per minute. The outlet gaswas passed through a second canister (the “trap”) having the sameadsorbent as the first canister. FIG. 7 shows the mass changes of thecanister and trap over time. It can be seen that the breakthroughcapacity of the canister is about 234 g of desflurane, while the maximumcapacity is 369 g of desflurane. In this case, breakthrough is deemed tobe the point when the weight gain in the trap exceeds 5 grams.

In a similar experiment, sevoflurane, at a concentration of 2% by volumein nitrogen, was passed through a canister of 1,100 g of adsorbent at arate of 2 liters per minute. The outlet gas was passed through a traphaving the same adsorbent as the canister. FIG. 8 shows the mass changesof the canister and trap over time. It can be seen that the breakthroughcapacity of the canister is 378 g of sevoflurane, while the maximumcapacity is 461 g of sevoflurane.

Example 2

The breakthrough and maximum adsorption capacities of a canistercontaining layers of two adsorbents was determined for sevoflurane. Acanister was provided with about 550 grams of a first adsorbent andabout 550 grams of a second adsorbent. The two adsorbents were keptseparated and not mixed. Gas passing through the canister would firstcontact the first adsorbent and then contact the second adsorbent. Thefirst adsorbent was a silica adsorbent with an average pore size ofabout 6 angstroms, a specific surface area of about 400 m²/g, and lessthan about 1.0 wt % Al₂O₃. The second adsorbent was an amorphous silicaadsorbent with an average pore size of about 20 angstroms, a specificsurface area of about 750 m²/g, and less than about 1.0 wt % Al₂O₃. FIG.9 shows the mass changes of the canister and trap over time. It can beseen that the breakthrough capacity of the canister is 172 g ofsevoflurane, while the maximum capacity is 237 g of sevoflurane.

Example 3

Multi-canister setups were evaluated for optimization of the collectionof anesthetics. In this procedure, two canisters of adsorbent wereplaced in series and subjected to routines that would likely be carriedout in a normal operating room. Table 2 describes the routines for each“day” in the operating room. Each loading period was separated by a 5minute purge of 10 L/min of nitrogen gas. Furthermore, an “idle” periodof 30 minutes after every post-operation purge was included, whichrepresented the inactive period between operations.

TABLE 2 Total loading (h) Day Case Description Sevoflurane Desflurane 1Load with 2% sevoflurane for 2 hours, 6 0 repeat 3 times. 2 Load with 2%sevoflurane for 2 hours, 4 2 repeat 2 times. Load with 6% desflurane for1 hours, repeat 2 times. 3 Load with 2% sevoflurane for 1 hours, 3 3repeat 3 times. Load with 6% desflurane for 1 hours, repeat 3 times. 4Load with 2% sevoflurane for 1 hours, 2 4 repeat 2 times. Load with 6%desflurane for 2 hours, repeat 2 times. 5 Load with 6% desflurane for 2hours, 0 6 repeat 3 times.

A trap was placed in series after the two canisters. The trap was alsomonitored for changes in weight. Table 3 shows the weight changes of thethree canisters at the end of each “day”.

TABLE 3 Weight gain (grams) Day Canister 1 Canister 2 Cumulative Trap 1151 1 152 0 2 349 20 369 −2 3 377 235 612 3 4 365 372 737 123 5 353 419772 174

In comparison, a 1-canister system was evaluated using a similar setup.Using a 1-canister system, 353 grams of anesthetics were adsorbed. Itwould be expected that a 2-canister system would adsorb twice as much,or 706 grams. Since 772 grams of anesthetics were actually adsorbedusing a 2-canister system, a surprising additional 66 grams wereadsorbed when the two canister were placed in series. Given that thetotal amount of anesthetic used in these procedures was 946 grams, theadditional 66 grams represents an additional collection of about 7%. Itis believed that the first canister is driven to a maximum since itcontinues to be exposed to anesthetic while the second canister is alsocollecting anesthetics.

Example 4

The effect of the adsorbent composition on sevoflurane was evaluated byadsorbing sevoflurane on a variety of adsorbents. The various adsorbentshad varying compositions of SiO₂ and Al₂O₃. Table 4 shows five silicagel and zeolite adsorbents, with amounts of Al₂O₃ ranging from 20 wt %to <0.5 wt %. About 100 grams of sevoflurane was adsorbed onto theadsorbents and then subsequently desorbed for 4 hours using nitrogen attemperatures between 95° C. and 130° C. The composition of the resultingdesorbed mixture was determined by gas chromatography. Table 4 showsthat adsorption of sevoflurane increases and decomposition ofsevoflurane decreases as the amount of Al₂O₃ in the adsorbent decreases.

TABLE 4 Adsorbent #100 #200 #300 #400 #500 Al₂O₃ (wt %) 20 15-20 15 3<0.5% GC Analysis (%) sevoflurane 0.2 38.6 97.68 99.93 99.781,1,1,3,3,3- 3.6 47.1 2.23 0.06 0.02 hexafluoroisopropanol Others 96.214.3 0.09 0.01 0.2

In the preceding description, for purposes of explanation, numerousdetails are set forth in order to provide a thorough understanding ofthe embodiments. However, it will be apparent to one skilled in the artthat other arrangements and embodiments would be feasible.

The above-described embodiments are intended to be examples only.Alterations, modifications and variations can be effected to theparticular embodiments by those of skill in the art without departingfrom the scope of the application, which is defined solely by the claimsappended hereto.

The invention claimed is:
 1. A conservation valve for use with acollection system for collecting an anaesthetic agent, the conservationvalve comprising: a valve body having an inlet port, an outlet port, anda fluid passageway between the inlet port and the outlet port, the inletport connectable to a source of exhaust gas so as to allow the exhaustgas to flow through the fluid passageway, and the outlet portconnectable to the collection system; a sensor located upstream of thevalve body for detecting a percentage content of anaesthetic agentwithin the exhaust gas, the percentage content of the anaesthetic agentbeing indicative of the level of anaesthetic agent being present withinthe exhaust gas; wherein the sensor generates an electrical signal tooperate the valve body to close the fluid passageway when the percentagecontent of the anaesthetic agent is below a predetermined level toisolate the exhaust gas from the collection system, wherein theanaesthetic agent is a halogenated hydrocarbon.
 2. The conservationvalve of claim 1 wherein the sensor comprises: an electrical currentgenerator for passing a current through the gas stream; a conductivitysensor for determining the thermal conductivity of the gas stream basedon the current passing through the gas stream; a processor for comparingthe thermal conductivity with predetermined values to determine ifhalogenated hydrocarbons are present in the gas stream.